Designing modern aqueous batteries

In the pursuit of more reliable and affordable energy storage solutions, interest in batteries powered by water-based electrolytes is surging. Today’s commercial aqueous batteries lack the energy density and cycle life required to compete in the fast-growing transportation and grid storage sectors, but this will change as new materials and cell design strategies are developed. Many of the constraints of traditional aqueous batteries have been alleviated by innovations such as selective membranes, lean-water electrolytes and new types of electrode reactions. As a result, an unprecedentedly broad range of electrode chemistries may be paired in previously impossible ways via modular cell designs to achieve performance metrics unattainable by traditional aqueous batteries. These innovations, however, change the properties for which aqueous batteries are traditionally known, and may result in compromises. This Review starts by examining the historical evolution of aqueous batteries, summarizing their essential merits and limitations. It then analyses how modern chemistries and cell designs may further strengthen the merits of aqueous batteries and address their limits while sometimes compromising prior merits, providing a holistic and critical overview of modern aqueous battery design. The emergence of new materials and cell designs is enabling the transition of aqueous batteries into competitive candidates for reliable and affordable energy storage. This Review critically examines the scientific advances that have enabled such a transition and explores future research prospects.